HR: 1340h
AN: AE23A-0914 INVITED    [Abstracts]
TI: Origin and Evolution of 'Sprites': Cause and Mechanism
AU: * Kikuchi, H
EM: hkikuchi@mars.dti.ne.jp
AF: Institute for Environmental Electromagnetics, 3-8-18, Komagome, Toshima-ku, okyo, 170,
AB: Recent observations of cloud-to-ionosphere discharges have led to a variety of appearance besides lightning to aurora transition. One of them is a modified form of eBall Lightningf, so-called gSpritesh termed by ionospheric physicists. This paper aims to explain a sequence of processes to manifestation of this phenomenon on the basis of eElectrohydrodynamics in Dusty and Dirty Plasmasf with novel physical concepts of eElectrical Cusp-Reconnectionf and eCritical Ionization Velocitiesf. Most of cloud-to- ionosphere discharges is initiated by electric reconnection in principle with global lightning activity. Their bipolar nature with much higher occurrence rate to positive cloud-to-ground flashes than to negative c!oud-to-ground flashes indicates that the cloud shape and charge distribution is thought to be inclined and extended rather horizontally with a sequence of cusped charge distributions or horizontal double layers. Such a horizontal extent of cloud clusters is possibly due to stratospheric jet streams on the topside of clouds in a way similar to the cloud and charge distributions in a coastal region of the Sea of Japan during winter, although the scale is much 1arger. This enables us to apply a scenario similar to triggered lightning for winter thunderstorms, based on the EHD concepts, electric reconnection and critical ionization velocities. We are now concerned with a leader ascending from a topside cloud that is the same as usual cases of the cloud-to-ground discharge in appearance and shape until some altitude. As it approaches the ionosphere, however, the atmospheric pressure goes less and less. Accordingly, its appearance should be gradually changing. As a result, there may be a chance for it to be forced to stop. A possible scheme with a whole process for 'sprites' formation is just like that. In view of the fact that 'sprites' are observed in much higher correlation with positive cloud-to-ground flashes than negative cloud-to- ground flashes directly underneath the thunderclouds, its upward leader is regarded as a positive leader. When this positive leader is ascending with decreasing gas pressure, its velocity is always limited up to its critical velocity or less, since it transfers to some charged identity with electrostatic energy. In this way, possible formation of ball and/or bead lightning, termed as `Sprites' could be expected. This is a formation mechanism of column- or bead-like ba11 and/or bead lightning, namely the so-called `Sprites'.
DE: 0343 Planetary atmospheres (5210, 5405, 5704)
DE: 0654 Plasmas
DE: 1704 Atmospheric sciences
DE: 2159 Plasma waves and turbulence
DE: 7800 SPACE PLASMA PHYSICS
SC: Atmospheric and Space Electricity [AE]
MN: 2007 Fall Meeting